The FCC is investigating AT&T's sudden 911 outage

The Federal Communications Commission (FCC) is investigating a outage of 911 emergency service that affected some AT&T Wireless customers in several states on Wednesday night.

The outage, which lasted about an hour, prevented affected customers from making 911 calls. FCC chairman Ajit Pai announced that FCC public safety staff would look into the cause.

It was not immediately clear how many customers were affected by the outage.

During the outage, some police and fire departments across the country urged affected AT&T users via Twitter to call mainline non-emergency phone numbers, rather than 911, until the problem was addressed.

However, unlike 911 calls, mainline phone calls do not show the caller's location, as noted by the Arlington Fire Department: "Our ability to see the location of a 9-1-1 caller is not available on the non-emergency line, so please give your address," the department said in a tweet Wednesday night.